Citric Acid and Endangered Hoary Bats

The ‘ope’ape’a or Hawaiian hoary bat gets its name from its heavy fur coat and white-tipped ears that give it a frosted look. This solitary bat species roosts in trees and is the only native land mammal in Hawaii. The Hawaiian hoary bat was listed as an endangered species in 1970 and its population continues to be impacted by loss of habitat, predation, and pesticide use.

Spray applications of citric acid, a registered minimum risk pesticide, are used to control invasive coqui frog populations on Hawaii. To ensure these applications do not negatively impact the endangered hoary bat, NWRC researchers conducted field and laboratory experiments using the more common big brown bat as a surrogate species.

“Hoary bats are an important part of Hawaii’s ecosystem,” states NWRC researcher Dr. William Pitt. “We want to ensure that management efforts to control invasive species on the islands are safe for the bat and other native species.”

Researchers studied the effects of citric acid on surrogate big brown bats. Results showed citric acid was toxic to the bats when 0.10 milliliters or more solution was ingested. However, bats sprayed with 5 milliliters of citric acid solution, did not show signs of intoxication from licking, grooming or direct skin absorption. Based on observations, researchers believe Hawaiian hoary bats are at very low risk from harmful exposure of citric acid during frog control operations.